Phonetics. the act or process by which a sound becomes identical with or similar to a neighboring sound in one or more defining characteristics, as place of articulation, voice or voicelessness, or manner of articulation, as in

early 15c., "act of assimilating," from Old French assimilacion, from Latin assimilationem (nominative assimilatio) "likeness, similarity," noun of action from past participle stem of assimilare (see assimilate). Psychological sense is from 1855.